Abstract : The effects of chemical etching on the tensile strength of commercial boron/tungsten (B/W) fibers were investigated. Fibers with as-received diameters of 203, 143, and 100 microns (7.98, 5.64, and 3.95 mils) were etched to diameters as small as 43 microns (1.7 mils). The etchings generally resulted in increasing fiber tensile strength with decreasing fiber diameter. And for the 203-microns (7.98-mil) fibers there was an accompanying significant decrease in the coefficient of variation of the tensile strength for diameters down to 89 microns (3.5 mils). Heat treating the 203-microns- (7.98-mil-) diameter fibers above 1173 K in a vacuum caused a marked decrease in the average tensile strength of at least 80 percent. But after the fibers were etched, their strengths exceeded the as-received strengths. Other 203-microns (7.98-mil) fibers, retrieved from an aluminum matrix, showed increases in strength due to etching that were somewhat similar to those of the etched as-received 203-microns (7.98-mil) fibers. The tensile strength behavior is explained in terms of etching effects on surface flaws and the residual stress pattern of the as-received fibers. This work shows that B/W fibers with diameters <165 microns (6.5 mils) can be obtained with average tensile strengths >4.83 GN/m(2) (700 ksi) with a coefficient of variation of <5 percent. (AN)